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Date: Wed, 21 Nov 2012 20:18:55 +0000 From: Ben Hutchings <bhutchings@...arflare.com> To: David Woodhouse <dwmw2@...radead.org> CC: Jeff Garzik <jgarzik@...ox.com>, Jason Wang <jasowang@...hat.com>, "David S. Miller" <davem@...emloft.net>, <netdev@...r.kernel.org> Subject: Re: 8139cp: set ring address before enabling receiver On Wed, 2012-11-21 at 19:51 +0000, David Woodhouse wrote: > On Wed, 2012-11-21 at 13:12 -0500, Jeff Garzik wrote: > > > > What sticks out at me from the commit message? > > > > It was not tested on the famously quirky 8139 hardware at all. > > > > While I have not looked at the 8139C+ data sheet in a while, sometimes > > the hardware _did_ have a strange init order. > > > > As this works in a simulator but fails on real hardware, it seems like > > an obvious regression caused by an untested [on read hardware] patch. > > The data sheet (v1.6, from http://realtek.info/pdf/rtl8139cp.pdf ) says > in ยง6.33 (C+ Command Register): > "Enable C+ mode functions in C+CR register first, > => Enable transmit/receive in Command register (offset 37h), > => Configure other related registers (ex. Descriptor start address, > TCR, RCR, ...)." > > I understand the concern expressed in the offending commit message about > DMA happening to invalid addresses, and I'll look at the data sheet > harder to see when the DMA actually starts happening. But it definitely > seems that our current code isn't doing what the data sheet says. > > I wonder if I can find one of these lying around and stick it in a > machine with an IOMMU... You might be able to avoid disaster by doing: 1. Set MAC filter to drop everything 2. Enable RX DMA 3. Set RX DMA ring address 4. Set MAC filter according to current flags & multicast list I'm assuming, knowing nothing about this particular hardware, that the MAC filter register(s) will accept writes before RX DMA is enabled. Ben. -- Ben Hutchings, Staff Engineer, Solarflare Not speaking for my employer; that's the marketing department's job. They asked us to note that Solarflare product names are trademarked. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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